1. Field of the Invention
The present invention relates to a computer implemented monitoring method for measuring a thickness of a thin film in a multi-layer structure. The present invention particularly relates to the method for measuring film thickness using computer integrated manufacturing (CIM) system, a sub system for measuring film thickness in the CIM system. Further, the present invention pertains to control programs for controlling the sub systems for measuring film thickness. Further, the present invention relates to a method of manufacturing a semiconductor device using in-line monitoring according to this method for measuring film thickness.
2. Description of the Related Art
As degree of integration density of semiconductor integrated circuits such as large-scale integrations (LSIs) becomes higher, the number of wiring layers in a multi-level interconnection become larger and larger. In a case in which there are eight metallic wiring layers, it may be general to deposit around thirteen to fourteen interlayer insulation films, which must be formed corresponding number of production stages. Thus in-line monitoring of film thickness of multi-layer structure is extremely important.
The earlier procedure of measuring film thickness of three-layers stacked structure by using a light interference type thickness-measuring tool will be described as a simple example, using flowcharts of FIGS. 1 to 3, and the data flow diagrams of FIG. 4.
(a) First, in a step S901, a first film is formed on a substrate. Next in a step S902, using a thickness-measuring tool 6, white incident light is irradiated onto the substrate having the first film formed thereon. In a step S903, the thickness measuring tool 6 disperses light reflected from the substrate into its component wavelengths using a spectroscope and detects the intensity of the reflected light at each resolved wavelength using a photo detector. Further, in a step S904, a sequence of light intensity data detected by the photo detector are stored so as to establish a profile (x: wavelength, y: intensity) of an actual measured reflection spectrum by a control computer of the thickness-measuring tool 6. The interference of light waves, which have been reflected at the front and back side of the first film (at two boundaries with different optical densities) leads to periodical amplifications and extinction in the spectrum of a white continuum light. For example, plotting the actual measured wavelength along the abscissa and reflected light intensity along the ordinate, in a wavelength range of 200 nm to 800 nm, there is a serpentine profile having two peaks and two valleys.
(b) Next, in a step S905, a plurality of theoretical profiles of the reflection spectrums are calculated at the first film's thickness range (ta˜ta+Δta) registered in a first measurement recipe of the control computer of the thickness-measuring tool 6. Further, in a step S906, one of the profiles closest to the profile of the actual measured reflection spectrum of the first film attained in the step S904 is searched in the theoretical profiles of the reflection spectrums arithmetically calculated in the step S905. Then the thickness value, upon which the closest theoretical profile of the reflection spectrum to the actual measured reflection spectrum is derived, is determined as the film thickness TA. Afterward, in a step S907, this film thickness value is expressed as a film thickness value TA, L1, W1 of specific lots and wafers (Further, the film thickness value TA, L1, W1 is stored away in a management server 9, as shown in FIG. 4).
(c) In a step S911 of FIG. 2, a second film is formed on the first film. Next, in a step S912, using the thickness-measuring tool 6, white incident light is irradiated onto the substrate having the second film formed thereon. In a step S913, the thickness-measuring tool 6 disperses light reflected from the substrate using the spectroscope and detects the intensity of the reflected light at each resolved wavelength using a photo detector. Further, in a step S914, a sequence of light intensity data detected by the photo detector are stored so as to establish a profile of an actual measured reflection spectrum by the control computer of the thickness-measuring tool 6. The profile of the actual measured reflection spectrum represents the reflection at the boundary of the first and second films and the reflection at the boundary of the substrate and the first film, and expresses a complex serpentine profile. Although results depend upon the relationships of the material parameters and film thickness, plotting the actual measured wavelength along the abscissa and reflected light intensity along the ordinate, in a wavelength range of 200 nm to 800 nm there is generally a serpentine profile having three to four peaks and three to four valleys.
(d) In a step S915, a plurality of theoretical profiles of the reflection spectrums are calculated. Here, in addition to the second film's thickness range (tb˜tb+Δtb) registered in a second measurement recipe of the control computer of the thickness-measuring tool, the thickness range (ta˜ta+Δta) of the first film which is underneath the second film, must be included in the calculation. Next, in a step S916, one of the profiles closest to the actual measured film reflection spectrum of the second film attained in the step S914 is searched in the theoretical profiles of the reflection spectrums arithmetically calculated in the step S915. Then the thickness value, upon which the closest theoretical profile of the reflection spectrum to the actual measured reflection spectrum is derived, is determined as the film thickness TB. Afterward, in a step S917, this film thickness value is expressed as a film thickness value TB, L1, W1 of specific lots and wafers (Further, the film thickness value TB, L1, W1 is stored away in a management server 9, as shown in FIG. 4).
(e) In a step S921 of FIG. 3, a third film is formed on the second film. Next, in a step S922, using the thickness-measuring tool 6, white incident light is irradiated onto the substrate having the third film formed thereon. In a step S923, the thickness-measuring tool 6 disperses light reflected from the substrate using the spectroscope and detects the intensity of the reflected light at each resolved wavelength using a photo detector. Further, in a step S924, a sequence of light intensity data detected by the photo detector are stored so as to establish a profile of an actual measured reflection spectrum by the control computer of the thickness-measuring tool 6. The actual measured reflection spectrum represents the reflection at the boundary of the substrate and the first film, the reflection at the boundary of the first and second films, and the reflection at the boundary of the second and third films, and expresses a complex serpentine profile. Although results depend upon the relationships of the material parameters and film thickness, plotting the actual measured wavelength along the abscissa and reflected light intensity along the ordinate, in a wavelength range of 200 nm to 800 nm there is generally a serpentine profile having five peaks and five valleys.
(f) In a step S925, a plurality of theoretical profiles of the reflection spectrums are calculated. Here, in addition to the third film's thickness range (tc˜tc+Δtc) registered in a third measurement recipe of the control computer of the thickness-measuring tool, the thickness range (ta˜ta+Δta) of the first film which is underneath the second film, and the thickness range (tb˜tb+Δtb) of the second film which is underneath the third film must be included in the calculation. Next, in a step S926, one of the profiles closest to the actual measured reflection spectrum of the third film attained in the step S924 is searched in the theoretical profiles of the reflection spectrums arithmetically calculated in the step S925. Then the thickness value, upon which the closest theoretical profile of the reflection spectrum to the actual measured reflection spectrum is derived, is determined as the film thickness TC. Afterward, in a step S927, this film thickness value is expressed as a film thickness value TC, L1, W1 of specific lots and wafers (Further, the film thickness value TC, L1, W1 is stored away in a management server 9, as shown in FIG. 4).
As put forth above, for measuring the film thickness of layered structures by earlier technology, and even in cases of measuring the topmost layer of a layered structure, the film thickness of the underlying layer also had to be measured. Put simply, in cases having a three-layers structure that results after forming the second film on the first film and the third film on the second film, aside from measuring the film thickness range (tc˜tc+Δtc) of the third film, theoretical profiles of the reflection spectrums for film thickness ranges of the first (ta˜ta+Δta) and second (tb˜tb+Δtb) thin films must also be calculated. So in this earlier methodology, compared with a measurement in which film thickness of a single layer is measured by calculating theoretical profiles of the reflection spectrums of the reflection spectrum at a film thickness range (tc˜tc+Δtc) of a single layer in a structure such as the first film/substrate, in the measurement of a multi-layer structure, problems such as increased measurement time, and decreased measurement precision (occurrence of “value jump”, etc.) will arise. In recent LSI, multi-layer structure above ten to thirteen layers have become the norm, and the calculation of all of the theoretical profiles of the reflection spectrums for film thickness ranges of underlying respective layers of these multi-layer structure uses up computer memory resources, bringing the need for an extremely long measurement time period.
Further, although it is also possible to insert dedicated extra semiconductor wafers for the exclusive purpose of measuring respective film thickness, and measure respective film thickness of the corresponding level in each of the process steps in which each of the thin films is formed, but rising manufacturing costs, in the manufacturing generation in which high priced large diameter semiconductor wafers are employed, becomes problematic. In a situation having a multi-layer structure of above ten to thirteen layers, inserting extra semiconductor wafers within underlying film leads to serious increases in manufacturing costs, when switching over to a 200 mm to 300 mm diameter semiconductor wafer.
Further, in a light interference type thickness methodology, it is impossible to measure precisely a multi-layer structure encompassing adjacent two layers, each having identical or extremely close refraction indice, or it will generate a drop in precision of the measurement.